--> Neogene Evolution of Southern Los Angeles and Capistrano Basins, Newport to Oceanside: OCS Sale 95 Targets, by Steven B. Bachman and James K. Crouch; #91024 (1989)

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Neogene Evolution of Southern Los Angeles and Capistrano Basins, Newport to Oceanside: OCS Sale 95 Targets

Steven B. Bachman, James K. Crouch

The southern Los Angeles and Capistrano basins, adjacent to proposed lease tracts in OCS sale 95, display good structural and sedimentologic evidence of Neogene basin-edge evolution. Some aspects of basin evolution have been described previously, but we have reinterpreted several new structural and stratigraphic features.

Early Miocene major rifting and basin formation are indicated by the deposition of deep-water clastic sediments intercalated with coarse debris from the rapidly uplifting and eroding basin flanks. These early basins appear to be fairly long and narrow. A rapid lateral transition from nonmarine to deep-marine(?) sedimentation is found within the coarsest of these sediments, the San Onofre Breccia. This breccia, which probably marks the most rapid phases of basin formation, is quite time transgressive, with tongues ranging from the early to middle (or late?) Miocene.

As the basins widened and matured, clastic sedimentation was apparently restricted to smaller deep-sea fan systems, and the middle to upper Miocene Monterey Formation biogenic sediments were deposited in the deeper parts of the basin. However, the Monterey is intercalated with the San Onofre breccia and deep-water sands locally near basin flanks and submarine canyons. At about 5 Ma, deep-marine clastic sedimentation again dominated the basins, as extensive structuring occurred on both strike-slip faults and low-angle thrust systems; these structures are shown on offshore profiles in an accompanying poster session.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.